Atgeirs are spears as you know them. The spears in Valheim are hunter's spears, which were shorter thrown weapons similar to what you might know as a Javelin.

The whole point of spears is not "Range" The whole point of spears is simplicity. You can shove a spear in a peasants hands, and have an effective fighter, especially when you amass a thousand of them together.

A trained Spear fighter most often uses a broad-headed Partisan or halberd. These are much longer and completely different in balance, and are classified as polearms Just like the Atgeirs. Where as a spear is simply a thrusting weapon, a partisan or halberd behaves more like a dagger or axe on a long shaft, with a much wider range of lethal motion aside from just the thrust.